Butane isomerization process



De?- 26, 1944 A. B. LEONARD 2,366,117

BUTANE ISOMERIZTION PROCESS Filed oct. 5, 1942 BY @16am A TTORNE YS Patented Dec. 26, 1944 BUTANE ISOMERIZATIGN PROCESS Ancel B. Leonard, Bartlesville, Okla., assignor to Phillips Petroleum Company, a` corporation ot Delaware Y Application october .5, 1942, serial No. 460.842 s claims. (c1. 26o-sass) The present invention relates to a process for the production of isobutane from n-butane. More particularly the invention relates to' a process ot isomerizing n-butaneto isobutanefin the presence of a metal halide catalyst.

In the isomerization of n-butane to isobutane over a catalyst of aluminum chloride in the presence of hydrogen chloride as anactivator, the

principal reaction occurring is the conversion of n-butane to the lower-boiling isobutane. Also "produced in the reaction are small amounts of propane and pentane, 'and a corrosive aluminum chloride sludge.

It has been proposed heretofore in hydrocarbon conversions to maintain the` reacting hydrocartions, whereby the corrosive metal halide does not come into contact with the vaporizer.

Broadly the invention provides a method of, and apparatus for, isomerizing normal butane to isobutane over an aluminum chloride catalyst, removing the isobutane in the vapor form with rectification to return a substantial proportion of the butane to the catalyst, and with provision for supplying heat of vaporization to the hydrocarbons in the reaction vessel. The reboiling or heat of vaporization necessary is supplied without encountering the problem of corrosion of the' heating elements by reason of a novel feature of Y my invention which will be better appreciated bons under vaporizing conditions in the reaction zone, i. e., in contact with the catalyst, whereby the liquid hydrocarbon coming in contact with the catalyst is at its boiling point'at the pressure y of operation. The hydrocarbon having a lower boiling int is vaporized and withdrawn from the cata yst in the form of vapors together with some of the hydrocarbon of higher boiling point infequilibrium therewith. The vapors may be partly or totally condensed Vand returned-to the catalyst for further reaction. This principle has notto my knowledge been applied to the isomerizationof butanes using aluminum chloride asl a catalyst. The aluminum chloride and aluminum chloride sludge present Vin the reaction zone are,

very corrosive to heating elements, `making` it' impractical to thereby supply heat to theA reactants to maintain vaporizing conditions in the Y reaction zone. The present invention provides a novel and practical method of carrying, outa hydrocarbon reaction in the presence of aluminum chloride and is particularly adapted to the conversion of n-butane to isobutane.

An object of this invention'is to provide an improved process for the isomerization of hydrocarbons in the presen of a metalhalide catalyst. Another object of t s invention is to provide y an improved process for the conversion of nbutane vto isobutane in the presence of aluminum chloride.

Still another object of this invention isto provide such a process in which the .reactarit hydrofrom a consideration of the drawing illustrating this feature, taken in consideration with the iol-l lowing detailed description of my invention.

Y The drawing is a diagrammatic view ofthe apparatus of 'my invention. vWith reference to the drawingfthe'numeral` I designates a pump arranged to take butane from a suitable source, not shown in the drawing, and

pass it through the heater 2 sfeed for the process. From the heater 2 the butane may be passed through the line 3, the pump 4,l and the heater 5, into the base ofr tower 6. which tower will. be more fully described hereinafter. Alternatively,

the butane may be passed through the line 8 to saturators 8A or 8B, from which it may be .admitted to tower through the lines I0 and II. Butane from the heater 2 may be admitted di-l rectly to the tower 6 througl line I I by operation of valve l2. The tower 6 is divided into three main sections,

35 the catalyst section I3, a rectifier section above -the catalyst section, and a stripping section below the catalyst section. Solidaluminum chloridecatalyst iills the catalyst'section I3, being sup- .40 ported therein by `th`e Ioraminus'partition I4.

A perforated plate I5 is provided above the catalyst section for distribution of liquid hydrocarbons over Vthe Aaluminum chloride catalyst. A downpipe I6 extends through the catalyst bed to y carry over liquid in excess o! that' which will pass through thecatalyst Vbed proper. A vaporv pipe` I1' accomniodates vapors from the stripping vsection in excess .of the quantity which maybe conveniently passed through the catalyst section.'

'carbons are contacted with the catalyst under 50 Therelative ldistribution between the vapors in ydistillation' conditions.

Amost important object of this invention is to provide an improved method of reboiling hydrocarbone undergoing reaction in the presence of the catalyst `bed and in the vapor pipe is controlled by valve I '(A. The rectifying section of the tower abovethe catalyst bed is provided with y 4 suitablemeans' for obtaining intimate countera metal halide catalyst under distillation condi- 55 current contact of liquid and vapor. Conventhe top of the tower through line 23.

tional bubble cap trays, for example, are prefer-` able for use in this section; similarly, the stripping section below the catalyst section is provided with suitable means for obtaining multiple contact between liquids and vapors. Liquid from the base of the tower is withdrawnv through .the line I8. Vapors pass overhead from the tower through the line I9 to cooler 20, are condensed, and the condensate collected in the accumulator 2I. The' reflux to the tower is taken from the accumulator by a pump 22 and introduced into At a point intermediate the catalyst section and the top of the tower a stream of liquid hydrocarbons may be withdrawn throughv the pipe 2l to the pump 4, vaporized in the heater 5. and introduced as vapors to the stripping section at the-base of the tower. A.The .heater B provides heat necessary to vaporize the product andreiiux. KHydrogen chloride is introduced to the tower 8 through the line 25 entering the tower lyst section.

The products from the tower B containing hydrogen chloride are passed from the accumulator to the top of the 'fractionator through line 3|' by the pump 32 as reux. 'The remainder of the overhead from the fractionator 21, containing the hydrogen chloride, is passed through line 33 from which it is introduced to the tower 6 through line 25. Fresh.. hydrogen chloride enters the .system through the line- 34. Heat is supplied to the .baseof the fractionator' 21 by the heating coil a packed section of the fractionatcrassisting in separation of the higher-boiling hydrocarbons from the lower-boiling hydrocarbons. The isobutane formed in the catalyst section is vapor-y' ized, together with normal butanev in equilibrium with the normal butane-isobutane mixture, and these vapors pass upward into the rectifying section admixed with aluminum chloride vapors and Vapors from the Astripping plate I5 into-contact with the catalyst and with immediately below the cata- Waste. i

. The aluminum chloride Iremoved as sludge inv the waste line I8 is replenished by aluminum s very little overow through the pipe I6. Vapors from the stripping section may, under some operating conditions, interfere with the flow of liq uid downward through the catalyst and cause excessive overflowthrough the downplpe I6. This is avoided by by-passing the vapors in excess of those which may be handled inthe catalyst section through the vapor pipe I1; j

Aluminum chloride sludge and some pentane are formed in thereaction, and being higher boiling than the butanes are concentrated by the stripping action of thevapors supplied to the base chloride carriedl o ver from the saturator through the line III. The butane is passed to the saturator through the line 8 continuously 6r intermittently toreplenish the aluminum chloride in the catalyst section as needed. The isomerization taking place in the saturatoris .relatively negligible since the butane passes through the saturator v36. The higher-boiling hydrocarbon fraction ,I

comprising isobutane .as product is withdrawn from the fractionator through line 31.

In operation, the catalyst section is provided with a charge of aluminum chloride catalyst suitably supported. as by admixture withRaschig rings. The saturators 9B and 9A are charged with aluminum chloride and serve to saturate the heated butane with aluminum chloride when in A use. The saturators are used alternately, satuby the heater 2. By manipulation of the conas vapor at the base of the tower.

rator 9A being on stream while saturator 9B is recharged withl aluminum chloride and vice versa.. The butane feed is heated to an elevated temperature, generally below the boilingl point,

trol valves any or all of the butane may be passed through the saturator or passed directly to the towr through the valver I2 tothe line II.- Any desired part of the butane feed may be passed through the line 3 to the heater 5 and admitted tower. Liquid in excess of that whichwill pass through the perforations overdows into the pipe I6 and is carried thereby to the plate below the catalyst section. The catalyst section serves two functions: it acts as a catalyst chamber and as I'he heated in relatively small quantity or at a relatively high flow rate. Additional solid aluminum chloride may be added as necessary directly to the catalyst section of the tower.v

The vapors passing. upward from the catalyst sectionn comprise aluminum chloride vapor, nor- Amal butane, isobutane, propane, and hydrogen chloride. Due to the rectifying action the aluminum chloride vapors andmost of the n-butane A mixture, are relatively readily. condensed and-i fractionated from the hydrocarbons. I have found that ilve bubble plates will eifect'substan- Ati'ally complete removal of the aluminum chloride from the, hydrocarbons. -At a'point in the recti- Iviously, theliquid withdrawn from the tower may I be vtaken from any point in the tower 8 above the point at which thehydrocarbonsare substantially free of aluminum chloride vapors. However, since the isobutane isdesired as the overhead product of Vthe tower and is undesirable in large-percentages in the catalyst section, I prefer to withdraw the" hydrocarbons at the lowest point in the fractionatorrwhere the hydrocarbons are substantially free from aluminum'chioride vapors.

Generally the catalyst section is operated the tower throughl the pipe I8 as v the scope of the following appended claims.

The hydrocarbons are further rectified to concentrate the isobutane at the top ofthe tower and the n-butane is returned to the catalyst section. Suilicient of the n-butane-rich hydrocarbon is withdrawn from the tower through line 24 5 to supply the heat for reboiling the column.

The propane formed in the reaction is taken overhead with the isobutane, some n-butane, and the hydrogen chloride. In the fractionator 21 the propane, together with any other very volatile l hydrocarbons which may be present, and the hydrogen chloride are separated as overhead from the n-butane and isobutane, which latter are withdrawn as product from the bottom "of the iractionator. Hydrogen chloride and propane adl mixed therewith are recycled to the tower 6 through the line 25. Excess propane may be removed from the system. When its concentration# exceeds a predetermined value the propane appears in the bottom product of the fractionator; however, it may be removed when desirable by venting from the accumulator 30. While the rectiilcation of the hydrocarbons in the upper portion of tower 6 serves to concentrate the isobutane in the overhead product, I have found that it is generally undesirable to attempt to completely eliminate n-butane from the overhead product of tower 6. I have found that satisfactory results are obtained with about ten mol percent ofthe n-butane passing overhead with the isobutane and hydrogen chloride. I have found further that complete separation of n-butane from the overhead eiiiuents of the tower 8 is impractical, if not actually impossible, in a rectification step-in theA presence of the eiiluent vapors from the catalytic isomerization. My present invention has some very important advantages vover similar processes in the prior art. A bed-of solid aluminum chloride catalyst may be maintained in contact with n-butane at its boiling point. Pumping of corrosive aluminum chloride sludge for `reboiling is not necessary. The tower in which the reaction takes place is reboiled without subjecting the heating apparatus to corrosive aluminum chloride or sludge thereof. Other advantages of my invention will be apparen to those skilled in the art.

While I have illustrated and described in detail a specific embodiment of my, invention, other modifications will be suggested'to those skilled in the art. yWhile I have described the operation of my process with specific reference to aluminum chloride as the aluminum halide catalyst, the invention may be applied toisomerization in the presence of the other aluminum halide catalyst, particularly aluminum bromide and aluminum iodide. The foregoing detailed description of the preferred embodiment' of my` invention is not to be construed as limiting my invention to lessen-v I claim: l. A process for the conversion of n-butane to Visobutane which comprises introducing liquid n- ,main body of catalyst in saidbed whereby liquid n-butane ilows downward through the catalyst effecting conversion to isobutane; passing vaporous eiiiuent comprising isobutane, n-bu'tane, and aluminum chloride to a rectifying zone; removing a vaporous eiiiuent comprising concentrated isobutane substantially free from aluminum chloride from the rectifyingzone; condensing at least a part of said vaporouseiiiuent; returningl condensate to the rectifying zone effecting condensation of the aluminum chloride and at least part oi the n-butane; returning the condensed aluminum chloride and n-butane into contact with the catalyst; withdrawing a stream of liquid hydrocarbons, substantially free from aluminum chloride, from an intermediate point in said rectifying zone; heating said liquid hydrocarbons to vaporize at least a portion thereof, and passing said heated hydrocarbons into contact with the aluminum chloride catalyst at a lower elevation than the main body ci the catalyst in said bed whereby the hydrocarbon vapors rise through the catalyst countercurrent to the liquid n-butane feed.

2. A process ior the conversion of n-butane to isobutane which comprises introducing n-butane at a temperature in the region of its boiling point into contact with a bed of solid aluminum halide catalyst in a reaction zone, passing vaporous eiiluents of said reaction zone comprising n-butane, isobutane, and vaporous aluminum halide to a rectifying zone, removing a vaporous eiiiuent comprising isobutane substantially free from aluminum halide vapors overhead from said rectication zone, condensing at least a part of the vaporous etlluent from the` rectifying zone and f returning condensate to the rectifying zone etfecting condensation of aluminum halide and at least a part of the n-butane, returning the condensed aluminum halide and n-butane to the reaction zone, withdrawing from an intermediate point in said rectifying zone a stream of hydrocarbons comprising n-butane substantially free.

from aluminum halide, heating said hydrocarbons to vaporize at least a portion thereof, and passing .said heated hydrocarbons to said reactionzone chloride in a separate zone, prior to contact withthe bed of aluminum vchloride catalyst, to incorporate aluminum chloride in said feed.

ANGEL B. LEONARD. 

